combining audio

Is there a way to manage the audio levels through an app? Or is it more dependent on the phone's built in capabilities?

Right now at work I listen to a skype audio call from my house (for security) at a very low volume and then at a higher level I listen to music or podcasts, both sources going at the same time. When my dog goes nuts, the door is knocked on, or (in theory) if someone busted down my door, I notice the change in volume and sound, turn off my local media, and focus on what I'm hearing until the drama passes.

I ask because I would like to continue this setup when not at work, like say while running, where I again have earphones in and am normally listening to audio content. I would like to be able to have two pieces of audio: music combined with a skype stream or normal phone call, going at the same time like at work.

So is there a way to have two sources going at the same time, with the volume of each independently adjustable? Is this an app thing or a phone thing? Phone will be Sprint Hero. Has anyone tried this? Thanks for any suggestions.

I have a little bit of a hard time in following your somewhat chaotic use case.

I don't know how a Skype call is classified, but as far as I'm aware, you can separately adjust volumes for Phone, Media, and some others -- but I don't think you can adjust two simultaneously playing media sources, unless the media-playing app has its built-in volume control.